PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 519 
Aron (’11) publishes data showing in a few instances the brain 
weight in greatly stunted dogs practically equal to that in normal 
heavier dogs of the same age. However, no observations were 
made concerning the initial brain weight at the beginning of the 
experiment and the extent of the brain growth which apparently 
occurred during the underfeeding is therefore uncertain. 
It is interesting to note that Variot and Lassabliere (’09) 
found the growth of the brain in underfed infants to be retarded 
less than the growth in body weight, the brain thus increasing 
at the expense of other tissues of the body. This observation 
agrees with my own results for young albino rats. 
During severe starvation a slight decrease in the weight of the 
brain was noted by Bechterew (’95) in puppies and kittens, and 
by Hatai (’04) in young rats. Acute and chronic inanition in 
adult rats causes but little if any loss in absolute brain weight 
(Jackson, ’15b). A very complete summary of the literature 
bearing upon the effect of inanition upon the brain is given by 
Jackson (’15b). 
CEREBRUM 
If the percentages are calculated from the combined weight 
of the separate brain parts, it appears that the cerebrum (table 1) 
(telencephalon and diencephalon, excluding olfactory bulbs) 
during normal growth increases from an average of slightly more 
than 64 per cent of the entire brain at birth (sexes combined) 
to a relative maximum of approximately 71 per cent during the 
early part of the second week. Thereafter, although increasing 
in absolute weight, the cerebrum forms a progressively smaller 
proportion of the brain, decreasing to an average of approximately 
67 per cent (sexes combined) at three weeks, and to about 61 per 
cent at one year and later. My results agree fairly well with 
those of Hatai (15) for adult individuals of approximately 
similar body length, with those of Sugita (’17) for the rat during 
the first 150 days, and also with the unpublished data of Donald- 
son (personal communication). Slight differences appear which 
are presumably due partly to experimental error and partly to 
normal variability in the size of the brain segments. 
